In a phonologicalorthography, a grapheme corresponds to one phoneme. In spelling systems that are non-phonemic — such as the spellings used most widely for written English — multiple graphemes may represent a single phoneme. These are called digraphs (two graphemes for a single phoneme) and trigraphs (three graphemes). For example, the word ship contains four graphemes (s, h, i, and p) but only three phonemes, because sh is a digraph.

Different glyphs can represent the same grapheme, meaning they are allographs. For example, the minuscule letter a can be seen in two variants, with a hook at the top, and without. Not all glyphs are graphemes in the phonological sense; for example the logogramampersand (&) represents the Latin word et (English word and), which contains two phonemes.